This invention relates to a device for controlling the sweeping-angle of a fan and more particularly to a device suitable for controlling the amplitudes of the sweeping-angle when the fan sweeps.
Conventional fans can only work in two modes, either fixed mode (no sweeping) or sweeping mode. That is to say, it can only provide air flow either in a fixed direction or within a sectorial area corresponding to an unvariable sweeping angle. Fixed mode is rarely used even by only one person, because after hitting a person for quite a long time, the wind would make him feel uncomfortable, though it might make him feel cool in a relatively short time. If people are gathering within a relatively small area, the sweeping interval for sweeping mode for a conventional fan would be too long to satisfy them. So it is understandable that people need a fan which is capable of sweeping with adjustable and controllable sweeping angle at their will.
The sweeping device in the conventional electrical fan usually is a four-bar linkage. In order to change the amplitude of the sweeping angle, the length of one of the bars called the crank is changed. Previously, people suggested a scheme to perform such length change, in which a pin or slidable bar can freely move in a slot resulting in corresponding change of the crank length and the parameters of the four-bar linkage, so that the sweeping angle will be adjustable. It should be noticed that the pin or slidable bar is moved and positioned in a slot by the force resulting from a spring on the adjusting mechanism and therefore this will cause some problems. On one hand, it is desired that the elastic force caused by the spring and the friction force between the pin and slot should be as small as possible to make the motion of the pin or slidable bar easy. On the other hand, it is also desired that the above said forces should be large enough to withstand the reaction force caused by connecting bar during the rotation of the crank and therefore to ensure that the pin can be positioned and fixed securely after being adjusted. Unfortunately, it is very difficult to make a compromise especially because of the limited space in the gear box of the sweeping device. So either such a sweeping device based on above scheme will not be easy to adjust or the sweeping angle will shift from a preset value during operation.